For the transmission of digital signals, individual data values are conventionally assigned to signal-space points within an I/Q signal space. If an interference of the transmission channel is based upon white noise, that is to say, the transmission channel is an AWGN (additive white Gaussian noise) channel, a maximum possible spacing distance between the signal-space points is advantageous for the avoidance of interference. One conventional transmission method is the 8-PSK method (phase-shift keying). In this context, as presented in FIG. 1, eight signal-space points are arranged on a unit circle around the origin of the signal space. A uniform spacing distance between adjacent signal-space points is obtained. However, only a few signal-space points can be accommodated.
For the more efficient exploitation of the signal space, with the equally widely used QAM method (quadrature-amplitude modulation), further signal-space points are inserted between the origin of the signal space and the signal-space points disposed further outwards. Accordingly, for example, with a 16-QAM method, 16 signal-space points are accommodated on a uniform square grid within the signal space. Accordingly, FIG. 2 shows a 16-QAM constellation diagram.
However, if the transmission channel is not an AWGN channel, and the noise provides a different power density distribution, these constellations prove disadvantageous. Transmission channels frequently provide a high noise power density with low amplitudes and a low noise power density at high amplitudes of the noise signal.
Regarding the prior art, reference is made by way of example to U.S. Pat. No. 5,852,389. However, in this context, no modulation compression is implemented, but rather a pre-distortion.